Question

y varies directly as the square of x. When x = 2, y = 20. Find y when x = 4.

Answer 1

Time to translate ...

y = kx^2

is for the first sentence. Ready to substitute?

Answer 2

substitiute what ?

Answer 3

\[20 = k2^2 = 4k \rightarrow k = 20/4 = 5\]\[y = 5\times x^{2}\]

x = 4... so y = 5 * 4^2 = 80

Answer 4

With

y = kx^2

substitute x = 2, y = 20